(a) Field of the Invention
The present invention relates to a tapered roller wheel bearing assembly. More particularly, the present invention relates to a tapered roller wheel bearing assembly having a second undercut for dispersing stress concentrated on a first undercut formed at a flange base portion.
(b) Description of the Related Art
Generally, a bearing is disposed between a rotating element and a non-rotating element so as to smooth rotation of the rotating element. Various types of bearings such as a ball bearing, a tapered roller bearing, needle bearing, and so on are currently used.
A wheel bearing is one type of such bearings, and rotatably connects a wheel that is the rotating element to a vehicle body that is non-rotating element. The wheel bearing includes an inner ring (and/or a hub) connected to one of a wheel or a vehicle body, an outer ring connected to the other of the wheel or the vehicle body, and rolling elements disposed between the outer ring and the inner ring.
Balls or tapered rollers are used as the rolling elements of the wheel bearing. Wheel bearings using balls are applied to small vehicles, and wheel bearings using tapered rollers are applied to large vehicles such as buses, trucks and so on.
A conventional tapered roller wheel bearing assembly is illustrated in FIG. 1 to FIG. 3.
As shown in FIG. 1 to FIG. 3, the conventional tapered roller wheel bearing assembly 10 includes a hub 20, an inner ring 60, an outer ring 30, and first and second tapered rollers 40 and 50.
A hub flange 23 for mounting a wheel is formed at a side portion of the hub 20 and a stepped portion 26 is formed on the other side portion of the hub 20. In addition, a hub raceway 25 is formed on an exterior circumference of the hub 20 between the hub flange 23 and the stepped portion 26, and a flange base 24 is formed at a connecting portion of the hub raceway 25 and the hub flange 23. Typically, a cross-section of the flange base 24 is formed in a curved fashion. A bolt hole 29 is formed at a radial outer portion of the hub flange 23 and a bolt is inserted in the bolt hole 29 such that the wheel is mounted on the hub flange 23. In addition, a pilot 22 for supporting the wheel is protruded from a side surface of the hub 20 in an axial direction.
The inner ring 60 is press-fitted onto the stepped portion 26 and an inner raceway 62 is formed on an exterior circumference of the inner ring 60. After the inner ring 60 is press-fitted onto the stepped portion 26, an end portion 27 of the hub 20 is bent radially outwardly so as to catch the inner ring 60. Thereby, preload is applied to the first and second tapered rollers 40 and 50.
The outer ring 30 is spaced radially outwardly from the hub 20 and the inner ring 60 and encloses the hub 20 and the inner ring 60. First and second outer raceways 32 and 34 corresponding to the hub raceway 25 and the inner raceway 62 are formed on an interior circumference of the outer ring 30.
A plurality of first tapered rollers 40 is mounted between the hub raceway 25 and the first outer raceway 32 in a state of being mounted in a first retainer 42, and a plurality of second tapered rollers 50 is mounted between the inner raceway 62 and the second outer raceway 34 in a state of being mounted in a second retainer 52.
Meanwhile, in a case that the first and second tapered rollers 40 and 50 are mounted on the hub 20 and the inner ring 60, the hub raceway 25 and protruded portions positioned at both end portions of the hub raceway 25, the inner raceway 62, and protruded portions positioned at both end portions of the inner raceway 25 that may contact with the first and second tapered rollers 40 and 50 should be machined precisely. Generally, although edges of the tapered rollers are arched, raceways are not machined in an arched fashion but are machined in a straight fashion due to characteristics of machining. In addition, since machined surfaces of each raceway and machined surfaces of protruded portions positioned at the both end portions of each raceway form angles, an edge portion at which the machined surfaces are joined is difficult to be machined. To solve such problems, an undercut is formed at the edge portion at which the machined surfaces are joined. That is, a groove is formed in advance circumferentially at the edge portion at which the machined surfaces are joined for ease of machining.
However, if the undercut is formed for ease of machining, the wheel bearing assembly becomes weak against impact. Particularly, if instant impact or strong impact is applied through the hub flange 23, as shown in FIG. 4, stress is concentrated on the undercut 28 formed at the flange base 24 and crack may occur around the undercut 28 or the hub 20 may be damaged due to concentration of stress. Since the undercut 28 should be formed for ease of machining, means for dispersing stress that may be concentrated on the undercut 28 is necessary.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.